1. Field of the Invention
The present invention relates to a method for treating the pathophysiological effects of cerebral amyloidogenic diseases, such as Alzheimer's disease. More specifically, the method involves administering the (−) enantiomer of nilvadipine to oppose pathophysiological effects in the brain of animals or humans afflicted with diseases associated with cerebral amyloidosis, such as Alzheimer's disease, with reduced antihypertensive side effects compared to the racemic mixture of nilvadipine.
2. Description of Related Art
Alzheimer's disease (AD) is the most common neurodegenerative disorder of aging, afflicting approximately 1% of the population over the age of 65. Characteristic features of the disease include the progressive accumulation of intracellular neurofibrillary tangles, extracellular parenchymal senile plaques, and cerebrovascular deposits in the brain. The principal component of senile plaques and cerebrovascular deposits is the 39-43 amino acid β-amyloid peptide (Aβ), which is proteolytically derived from amyloid precursor protein (APP), a transmembrane glycoprotein.
APP is a single-transmembrane protein with a 590-680 amino acid extracellular amino terminal domain and an approximately 55 amino acid cytoplasmic tail. Messenger RNA from the APP gene on chromosome 21 undergoes alternative splicing to yield eight possible isoforms, three of which (the 695, 751 and 770 amino acid isoforms) predominate in the brain. APP undergoes proteolytic processing via three enzymatic activities, termed α-, β- and γ-secretase. Alpha-secretase cleaves APP at amino acid 17 of the Aβ domain, thus releasing the large soluble amino-terminal fragment α-APP for secretion. Because α-secretase cleaves within the Aβ domain, this cleavage precludes Aβ formation. Alternatively, APP can be cleaved by β-secretase to define the amino terminus of Aβ and to generate the soluble amino-terminal fragment β-APP. Subsequent cleavage of the intracellular carboxy-terminal domain of APP by γ-secretase results in the generation of multiple peptides, the two most common being 40-amino acid Aβ (Aβ40) and 42-amino acid Aβ (Aβ42). Aβ40 comprises 90-95% of the secreted Aβ and is the predominant species recovered from cerebrospinal fluid (Seubert et al., Nature, 359:325-7, 1992). In contrast, less than 10% of secreted Aβ is Aβ42. Despite the relative paucity of Aβ42 production, Aβ42 is the predominant species found in plaques and is deposited initially, perhaps due to its ability to form insoluble amyloid aggregates more rapidly than Aβ40 (Jarrett et al., Biochemistry, 32:4693-7, 1993). The abnormal accumulation of Aβ in the brain is believed due to either over-expression or altered processing of APP.
Aβ peptides are thus believed to play a critical role in the pathobiology of AD, as all the mutations associated with the familial form of AD result in altered processing of these peptides from APP. Indeed, deposits of insoluble, or aggregated, fibrils of Aβ in the brain are a prominent neuropathological feature of all forms of AD, regardless of the genetic predisposition of the subject.
Concomitant with Aβ deposition, there exists robust activation of inflammatory pathways in AD brain, including production of pro-inflammatory cytokines and acute-phase reactants in and around Aβ deposits (McGeer et al., J Leukocyte Biol., 65:409-15, 1999). Activation of the brain's resident innate immune cells, the microglia, is thought to be intimately involved in this inflammatory cascade. It has been demonstrated that reactive microglia produce pro-inflammatory cytokines, such as inflammatory proteins and acute phase reactants, such as alpha-1-antichymotrypsin, transforming growth factor β, apolipoprotein E and complement factors, all of which have been shown to be localized to Aβ plaques and to promote Aβ plaque “condensation” or maturation (Nilsson et al., J. Neurosci. 21:1444-5, 2001), and which at high levels promote neurodegeneration. Epidemiological studies have shown that patients using non-steroidal anti-inflammatory drugs (NSAIDS) have as much as a 50% reduced risk for AD (Rogers et al., Neurobiol. Aging 17:681-6, 1996), and post-mortem evaluation of AD patients who underwent NSAID treatment has demonstrated that risk reduction is associated with diminished numbers of activated microglia (Mackenzie et al., Neurology 50:986-90, 1998). Further, when Tg APPsw mice, a mouse model for Alzheimer's disease, are given an NSAID (ibuprofen), these animals show reduction in Aβ deposits, astrocytosis, and dystrophic neuritis correlating with decreased microglial activation (Lim et al., J. Neurosci. 20:5709-14, 2000).
Products of the inflammatory process in the AD brain therefore may exacerbate AD pathology. Furthermore, there is evidence that activated microglia in AD brain, instead of clearing Aβ, are pathogenic by promoting Aβ fibrillogenesis and consequent deposition as senile plaques (Wegiel et al., Acta Neuropathol. (Berl.) 100:356-64, 2000).
It also has been suggested that AD pathogenesis is due to the neurotoxic properties of Aβ. The cytotoxicity of Aβ was first established in primary cell cultures from rodent brains and also in human cell cultures. The work of Mattson et al. (J. Neurosci., 12:376-389, 1992) indicates that Aβ, in the presence of the excitatory neurotransmitter glutamate, causes an immediate pathological increase in intracellular calcium, which is believed to be very toxic to the cell through its greatly increased second messenger activities.
U.S. Patent Application No. 2005/0009885 (Jan. 13, 2005) (Mullan et al.) discloses a method for reducing Aβ deposition using nilvadipine, as well as methods of diagnosing cerebral amyloidogenic diseases using nilvadipine. However, U.S. Pat. No. 4,338,322 describes nilvadipine for its antihypertensive effects. Nilvadipine (NIVADIL™) has received regulatory approval in Ireland for treatment of hypertension at a dose of 8 mg per day, or 16 mg per day if an adequate anti-hypertensive effect is not achieved with 8 mg per day. See also U.S. Pat. No. 5,508,413, which discloses antihypertensive effects of the (+)-enantiomer of nilvadipine. Racemic nilvadipine and its effect on regional cerebral blood flow in human subjects are reported in Hanyu et al. (Nuclear Medicine Communications, vol. 28, no. 4, pages 281-287, April 2007).
Despite the reports indicated above, there exists a need for a prophylaxis for the inexorable progression of brain degeneration that is a hallmark of AD, wherein the prophylaxis addresses the Aβ deposition, Aβ neurotoxicity, microglial-activated inflammation, and altered or overexpression of APP that is seen in AD patients with therapeutically effective treatment with minimal side effects such as unwanted or excessive reduction in blood pressure.